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Detecting pot use in drivers will be tricky

Michael Swensen for The Boston Globe/File

In the coming year, police in Massachusetts will likely have to deploy a litany of tests before arresting drivers for being high on marijuana, state officials said Friday.

Because there’s no accurate breathalyzer for cannabis use, officers will probably need to use a combination of their observations, roadside assessments, saliva tests, and a 12-step expert evaluation at the police station, said Walpole police Chief John Carmichael, a member of the state’s commission on operating under the influence.

“One [test] in and of itself doesn’t mean anything, but all of those things together can,” Carmichael said.

As recreational marijuana stores start to open for business throughout the state, officials are working with urgency to address a potential rise in stoned drivers on the roads. The commission must make recommendations to state lawmakers by Jan. 1.


Julie Johnson, director of research for the Cannabis Control Commission, told officials it could take about five years before a marijuana breathalyzer that detects impairment levels is available. In the meantime, she said, the most reliable method of determining someone’s impairment due to cannabis has been through drug recognition experts, called DREs, who are police officers who complete several weeks of specialized training.

“We think DREs are the best, as far as validity, that we have,” Johnson said.

There are about 150 drug recognition experts on police forces statewide now, officials said. About 73 percent of law enforcement agencies have at least one such expert on staff.

Johnson said she would like the state to have one for every 1,000 residents in every town or city, which could mean hundreds or thousands more would need to be trained.

Carmichael said he would like the state to at least double the current number, adding that New Jersey has about 400 such officers.

The drug recognition training is expensive, Carmichael said, in part because departments often must pay overtime to cover the shifts left open for weeks. He said that some of the 20 percent tax revenues from marijuana sales should help cover such costs.


Other commission members agreed that police forces need more drug recognition experts.

“Certainly, it’s going to cost a lot more money, however it’s looked at now as the most effective tool that we can use at this point,” said Peter Elikann, a criminal defense attorney. “Those cases are the hardest to prosecute. People usually get off on those because the techniques are not what they should be.”

Saliva tests are easy and fast for roadside use, but they’re not as effective at detecting marijuana impairment as an alcohol breathalyzer, said Samantha Doonan, a research analyst. The saliva-testing tools can cause a false positive in some chronic marijuana users, she said, and can fail at detecting marijuana by users who ingest capsules or pills that don’t contaminate the mouth.

Other biological tests such as urine and blood only show whether someone consumed cannabis in the past hours, days, or weeks, Doonan said — not whether the person was high at that moment.

Drivers have the right to refuse testing. To address that, Carmichael said the commission should recommend that drivers who show signs of drug impairment and refuse to be evaluated face an automatic license suspension, the same as drivers who refuse to blow into alcohol breathalyzers.

While police can easily take a suspected dangerous driver off the road, Carmichael said, making a conviction stick is another matter. While scientists agree that blood-alcohol content is a valid measure of a person’s drunkenness, Doonan said, there is no consensus about the amount of marijuana detectable in the blood as an indicator of how stoned a person is. Some people may show high levels of marijuana and not be impaired, while others may be stoned and have no detectable marijuana in their blood.


The state’s highest court found last year that standardized field sobriety tests — standing on one leg, walking and turning, and others — alone were insufficient to determine whether someone was impaired on marijuana.

Researchers have found that cannabis can impede key driving skills, such as cognitive functioning, reaction times, and the ability to multitask. Mixing pot and alcohol can be especially dangerous.

Studies have found mixed results on whether legalizing marijuana made roads less safe. Last year, the Insurance Institute for Highway Safety found that collision claim frequencies in Colorado, Washington, and Oregon were about 3 percent higher after they legalized pot than would have been anticipated without legalization. But a study in the American Journal of Public Health found no increase in traffic crash deaths in Colorado and Washington, relative to similar states, after legalization.

The commission will meet again next week to finalize its recommendations.

Naomi Martin can be reached at Follow her on Twitter at @NaomiMartin.